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There is a newer version: 3.6.2_1

// SPDX-License-Identifier: BSD-3-Clause
// Copyright (c) 1999-2004 Brian Wellington ([email protected])

package org.xbill.DNS;

/**
 * Constants and functions relating to flags in the DNS header.
 *
 * @author Brian Wellington
 */
public final class Flags {

  private static final Mnemonic flags = new Mnemonic("DNS Header Flag", Mnemonic.CASE_LOWER);

  /** query/response */
  public static final byte QR = 0;

  /** authoritative answer */
  public static final byte AA = 5;

  /** truncated */
  public static final byte TC = 6;

  /** recursion desired */
  public static final byte RD = 7;

  /** recursion available */
  public static final byte RA = 8;

  /** authenticated data */
  public static final byte AD = 10;

  /** (security) checking disabled */
  public static final byte CD = 11;

  /** dnssec ok (extended) */
  public static final int DO = ExtendedFlags.DO;

  static {
    flags.setMaximum(0xF);
    flags.setPrefix("FLAG");
    flags.setNumericAllowed(true);

    flags.add(QR, "qr");
    flags.add(AA, "aa");
    flags.add(TC, "tc");
    flags.add(RD, "rd");
    flags.add(RA, "ra");
    flags.add(AD, "ad");
    flags.add(CD, "cd");
  }

  private Flags() {}

  /** Converts a numeric Flag into a String */
  public static String string(int i) {
    return flags.getText(i);
  }

  /** Converts a String representation of an Flag into its numeric value */
  public static int value(String s) {
    return flags.getValue(s);
  }

  /**
   * Indicates if a bit in the flags field is a flag or not. If it's part of the rcode or opcode,
   * it's not.
   */
  public static boolean isFlag(int index) {
    flags.check(index);
    return (index < 1 || index > 4) && (index < 12);
  }
}